Descriptions provided hereinafter are merely background information relating to the present disclosure, but are not related to the related art.
Pillar members of vehicles are provided as members supporting the roof of a vehicle and as structural members of a vehicle directly affecting the safety of a driver when a vehicle is overturned.
As illustrated in FIG. 1, pillar members may be disposed to be connected to a roof of a vehicle. In addition, pillar members may be disposed between a windshield and a side window of a vehicle, between a front door and a rear door on a side thereof, between the rear door and a rear window, or the like.
As collision regulations have been tightened in terms of the safety of vehicles, the requirements for load bearing performance of pillar members have gradually become stricter. Thus, high strength is required in pillar members.
However, as illustrated in FIG. 2, in the case of pillar members of the related art, pillar members having closed cross-sectional portions are formed in such a manner that two press members are cast in an interior of an outer panel forming a vehicle body of a vehicle, and welding flanges formed on opposing end portions of press members are bonded by welding.
As such, in a case in which pillar members are manufactured using a pressing method of the related art, a cross section of pillar members may be significantly large, in order to secure sufficient load bearing performance.
In detail, in a case in which pillar members of the related art are applied to pillar members formed between the windshield and the side window, driver visibility may be obstructed by pillar members having a cross section, an area of which has been increased, thereby causing traffic accidents.
In addition, giga-class ultra-high strength steel may not be cast using a press casting method of the related art.
Thus, a suggestion for manufacturing ultra-high strength steel using a method, such as a hot press forming (HPF) method, has been considered, but the HPF method has a problem in which manufacturing expenses are significantly increased.
Thus, it is required to consider manufacturing structural members using a roll forming method in which the degree of size precision is high, substantially no scrapping and wear of a roll occurs, thereby significantly economically manufacturing products having a uniform cross section shape and a relatively long length.